Products and processes for producing steel alloys using an electric arc furnace

ABSTRACT

Feedstock for steel production in an arc furnace comprising a first influent comprised of cured and bound solid pieces comprised of a mixture of carbon materials, including a dominate amount of low grade coal, and a second influent comprised of ferrous material comprising scrap iron and/or steel for full reaction with the carbon material to produce the alloy.

FIELD OF THE INVENTION

The field of this invention relates to recovery of steel alloys in anelectric arc furnace using ferrous material, primarily low grade coal,cured and bound into solid pieces and a carbon fixing binder.

BACKGROUND

Hard or metallurgical coke is used in blast furnace production of steel.Metallurgical coke per se is not ordinarily used in electric arc furnacebecause, among other things, such is not cost effective. Electric arcfurnace secondary steelmaking differs basically from primary steelmakingfrom iron ore in a blast furnace. Historically, soft coke is the carbonsource for electric arc furnace secondary production of steel from pigiron, direct reduction iron and salvage or scrap steel and iron, but isstill expensive and negatively impacts the environment.

In the past, little has been done to provide a less expensive buteffective source of carbon for secondary steel production using electricarc furnaces.

The present invention meaningfully addresses the need to provide a lessexpensive but highly functional source of carbon for secondarysteelmaking in electric arc furnaces. Carbon from different sources,primarily low grade coal, are combined, blended, formed and heat-treatedinto cured and bound solid electric arc furnace influent carbon pieces,which do not deteriorate or elutriate in an electric arc furnace. Thesolid pieces can also be customized, with certain additives, to meet thespecific demands associated with the diverse operations of variouselectric arc furnaces.

BRIEF SUMMARY AND OBJECTS OF THE INVENTION

In brief summary, the present invention addresses problems orshortcomings of the prior art. Cost-effective methods are providing forforming and using a composite carbon feedstock comprising small curedand bound solid pieces, such as pellets and briquettes, suitable forsecondary steelmaking in electric arc furnaces. The composite carbonsolid pieces primarily comprise low value crushed coal and a minoramount of coke breeze and/or petroleum coke. The cured and bound solidpieces comprise a first influent to an electric arc furnace and ferrousmaterial a second influent. Flux may be a third influent.

The make-up of the solid pieces can be customized, using certainadditives, to meet the specific demands associated with the diverseoperations of various electric arc furnaces.

With the foregoing in mind, it is a primary object of the presentinvention to cost-effectively provide reliable carbon feedstock forsecondary steelmaking in electric arc furnaces, which feedstockdominantly comprises low value coal formed, with other materials, intocured and bound solid pieces, and related methods.

A further important object is to provide solid cured and boundcarbon-providing pieces for cost-effective and reliable use in electricarc furnaces, the solid pieces predominantly comprising low value coalcombined with a lesser amount of coke breeze and/or petroleum coke, andrelated methods.

Another significant object of the invention is the provision ofcost-effective and reliable bound and cured small solid pieces as carbonfeedstock for secondary steelmaking in electric arc furnaces, such thatthe solid pieces comprise mostly low value coal augmented by some cokebreeze and/or petroleum coke to obtain a composition comprising 75-90%by weight of nominal fixed carbon coke, supplemented by additives suchas discarded revert materials to customize the solid pieces to meetspecific demands associated with the diverse operations of variouselectric arc furnaces, and related methods.

These and other objects and features of the present invention will beapparent from the detailed description taken with reference to theaccompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING

The Figure is a flow chart illustrating one presently preferred methodaccording to the invention.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENT

Steelmaking is an old technology and generally has heretofore combinedcarbon, in the form of coke and ferrous material in blast and electricarc furnaces (EAFs). Those with skill in the art declare that primarysteelmaking in blast furnaces differs significantly and basically fromsecondary steelmaking in EAFs. Broadly, the differences, among others,include the need for iron ore as the primary ferrous source andmetallurgical coke in blast furnaces compared to scrap metal and softcoke in EAFs.

The present invention is limited to EAF technology, to the exclusion ofblast furnace technology. More specifically, the present inventionsubstitutes small solid pieces, such as pellets and briquettes, for thesoft coke of the past as the carbon source for secondary steelmaking.Surprisingly, the solid pieces have proven to be effective and far lesscostly. The makeup and methodology of the solid pieces are explained indetail below.

As used herein, the term EAF includes the basic furnace and any and allladles used to first obtain pig iron and then steel, when such a systemis used.

Typically, the basic EAF is refractory lined and charged at the top whenopen. The main and sometimes exclusive source of ferrous material isrecycled scrap iron and steel, which is loaded into the top of the basicEAF essentially at the same time that the carbon source is also loadedinto the top. The scrap iron and steel are preferably pre-heated, beforeintroduction, to reduce costs. Off-gas from the EAF can be used topreheat the scrap.

Oxygen, in a very pure state, is supplied through a water-cooled lance,usually in three steps, i.e. (1) at the correct height well above thebath surface, (2) at a lower position once heat has somewhat melted thescrap metal and (3) finally substantial into the molten bath with a veryhigh velocity discharge blow. Flux, such as burnt lime (CaO) anddolomitic lime (MgO), may be added while the lance is above the bathsurface to increase slag production. Fluxes control the chemistry andsulfur and phosphorous capacity of the slag. Oxygen from the lancelowers the bath carbon content to the desired level for tapping. Areaction of oxygen with carbon in the bath produces carbon monoxide,which may burn in the EAF, if oxygen is available.

Phosphorus, sulfur, aluminum, silicon, manganese and carbon are removedby reaction with the oxygen to form oxides which become part of theslag. At the appropriate time, the slag is poured out of the furnacethrough a slag door.

Gaseous discharge by-products are processed as off-gas to reduceenvironmental contamination and to recover energy.

In one EAF system, the molten material produced in a basic furnace istransferred via a ladle to a ladle furnace, where additions are meltedand blended into the liquid steel being produced, such that theresulting steel has the properties desired by the producer prior toforming the steel product into the desired shapes. The basic furnace andthe ladle furnace are considered herein collectively as constituting asingle EAF.

The traditional mode of secondary steelmaking in EAFs has become costintensive. More specifically, the cost of traditional soft coke imposessome limitations on and higher costs for steel derived from EAFs.

The present invention meaningfully addresses the need to provide a lessexpensive but highly functional source of carbon for secondarysteelmaking in EAFs. Carbon from different sources, primarily low gradecoal, are combined, blended, formed and heat-treated into cured andbound small solid EAF influent carbon pieces, which do not deteriorateor elutriate when used in electric arc furnaces. The solid pieces, asexplained here and after, can also be customized, with certainadditives, to meet the specific demands associated with the diverseoperations of various EAFs.

The reliability and cost effectiveness of the present invention centerson the use of low value crushed coal, to which a minor amount of coalbreeze and/or petroleum coke is added. The composition is bound andcured in the form of small solid pieces which, when placed in an EAF donot deteriorate prior to functioning in their steelmaking capacity anddo not elutriate. The solid pieces and the methodology by which thesolid pieces are formed combine to define, in large measure, the presentinvention.

Since EAFs produce an array of steels having various properties, thepresent invention includes additives in the solid particles selectedfrom discarded revert materials and other elective materials.

While not critical, in addition to scrap iron and steel as the ferrousmaterial for EAFs, in accordance with the present invention, a lesseramount of iron ore may be used, as would be apparent to those skilled inthe art.

Reference is now made to the drawing for purposes of providing greaterdetail concerning the present invention. The sources of carbon 10,comprises clean, crushed and sized low value coal having a low moisturecontent, typically in the range of 4-12% by weight, which is depicted at12 in the drawing. This low value coal 12 is critically selected tocomprise 72-75% by weight of the solid shapes being produced. Combinedwith the coal is a far lesser amount of coke breeze and/or petroleumcoke 14 on the order of 10-17% by weight. Flux 16 of one or more typesselected by those skilled in the art may also be added when appropriatefor the steel selected to be produced. Also, in certain applications,leftover revert materials 18, comprised of carbon content, discardedfrom blast furnaces and/or EAFs may be added to the initial mix fromwhich the solid shapes are derived.

The low value coal 12 preferably has a sieve size on the order ofone-quarter inch minus, although that is not critical. The coalparticles are derived from the bituminous, subbituminous, lignite andprocessed waste coal fines, as appropriate and available and asdetermined by those skilled in the art.

Low value coal is cleaned, unwanted debris is removed and the watercontent is lowered to an acceptable level for purposes of producingreliable and effective solid pieces. The washing, removal of debris andreduction in water content in the crushed low value coal are allaccomplished using well known technologies. Accordingly, no furtherdescription of how the coal is cleaned, washed and reduced in moisturecontent is necessary. The use of a predominant amount of low value coalin creating a composite source of carbon in the form of bound and curedsolid pieces to be used in EAFs provides reliability in secondarysteelmaking and provokes a meaningful reduction in the cost ofmanufacturing steel in EAFs.

The low value coal 12 and the coke breeze and/or petroleum coke 14 areintroduced essentially at the same time into a commercially availableblender 20 together with a carbon fixing binder 22, such as coal tars,pitches derived from destructive coal distillation, partially reactedStyrene oligomers or any other binder capable of functioning as a carbonfixing binder. The binder 22 is introduced into the blender 20 duringmixing. While the amount of binder 22 used in any batch varies with thequality of the coal, usually the binder will comprise 10-18% by weightof the mixture at 20. After the ingredients placed in the blender 20have been thoroughly mixed so as to be essentially homogeneous, theresulting mixture is then formed into green solid shapes shown at 24. Ithas been found that the coke 14 acts as a spine to hold the green piecestogether until they are fired. The coke 14 thus acts as a temporaryadhering agent holding the coal and the binder together as a semi-solidconglomerate until the green solid pieces are fired. Techniques forforming green semi-solid material into green pellets and briquettes arewell known and need not be further described here. The solid shapes mayalso be created using extruders and/or dies and presses. As a result,the blended composition constitutes separate small green solid pieces,which are next introduced into a furnace, preferably a muffle furnacehaving a moving bed on which the green solid pieces are transportedthrough the calcining furnace 26 so as to be first pre-heated to atemperature of about 550° F. and then, in an anaerobic phase of theoven, to 1000° C., where volatile materials are evaporated. The volatilegases 28 are then condensed and distilled, at 30, create high valueproducts, including coal tar, liquid hydrocarbons 32 and off gas 34 foruse in the plant or elsewhere, as deemed appropriate. For example, thelighter gases can fuel equipment used to generate electricity for use inthe plant. In the third phase of the muffle furnace, the solid piecesare anaerobically cooled. The time duration during which the green solidpieces are heat-treated in the muffle furnace should be on the order ofone hour, but such is not precisely critical. In any event, theresulting cured and bound solid pieces produced should be amplyheat-treated in the furnace so as to be reliable and not break down orelutriate during use in secondary steelmaking.

The resulting solid cured and bound pieces 36 comprise a composite formof fixed carbon composite coke having a 75-90% fixed carbon content toeffectively function for the purpose intended. The cured and bound solidpieces 36 may be stored in inventory or may be directly used in an EAF,shown at location 38 in the drawing, to which ferrous materialconsisting primarily of scrap iron and steel 40 is also added as aninfluent to the EAF 38. Minerals, such as flux 42, may also be added inaccordance with choices made by those skilled in the art in order toproduce the desired type of steel from the EAF 38.

The resulting steel product is formed into the desired shape or shapes.The effluent 44 from the EAF 38 is molten steel.

The cured and bound solid pieces issuing from 36 are preferred to havethe following characteristics: moisture not to exceed 2.5%; sulfur notto exceed 2.0%; volatile residue not to exceed 2.5%; ash not to exceed8.0%; and carbon not less than 85.0%.

The solid piece carbon product 36, made in the foregoing manner, offersseveral important qualities to steel producers. First, the product canbe manufactured to meet precise attributes specific to each producer'sneeds. The product can be customized or blended with fluxing agents andother materials specific to the needs of each individual mill.

During experimental testing, the cured and bound solid pieces were foundto help protect vital mill components and to potentially increase theefficiency of mill operations by reducing individual batch meltingtimes. The manufacturing process has the ability to produce variouslysized materials, using extrusion, pelletizing or briquetting techniques,to customize the solid pieces for individual customer needs.

Experimental Testing examples are set forth below:

Example 1

A supply of solid cured and bound pieces were prepared in accordancewith the process set forth above and having the characteristics also setforth above. Approximately 300 lbs. of these solid pieces wereintroduced into an EAF together with scrap steel, in two heats. Theresulting steel was of suitable high quality and no contra results tookplace.

Example 2

Two one-thousand pound batches of solid carbon pieces were made fortesting in an EAF, using the process and having the characteristicsrecited above. The solid pieces were utilized in several experimentaltests. Test results were positive and solid pieces were deemedfunctional in the electric arc melt operation. The resulting steel wasof high quality.

While this invention has been described with reference to certainspecific embodiments and examples, it will be recognized by thoseskilled in the art that many variations are possible without departingfrom the scope and spirit of this invention, and that the invention, asset forth in the claims, is intended to cover all changes andmodifications of the invention which do not depart from the spirit ofthe invention.

What is claimed and desired to be secured by Letters Patent is:
 1. Amethod of making one or more secondary steel products in an electric arcfurnace comprising the acts of: preparing blended, cured and bound solidsoft carbon pieces as an influent into the electric arc furnace, thesolid pieces comprising carbon material principally comprises of lowvalue coal particles, coke breeze and/or petroleum coke and a carbonfixing binder; providing ferrous material; introducing the soft carbonsolid pieces and the ferrous material into the electric arc furnace;heat-processing the solid pieces and the ferrous material to obtain theone or more secondary steel products therefrom.
 2. A method according toclaim 1 further comprising the act of causing the blended, cured andbound solid soft carbon pieces to comprise discarded revert material. 3.In combination: solid blended, cured and bound soft carbon solid piecescomprising of carbon materials for use in an electric arc furnace bywhich a steel alloy is obtained; the carbon materials predominantlycomprising low value coal particles and also comprising a non-dominateamount of coke breeze and/or petroleum coke; ferrous material for use inthe electric arc furnace with the solid pieces; the solid pieces furthercomprising by a carbon fixing binder.
 4. A combination according toclaim 3 wherein the solid pieces comprise, by weight, the followingcharacteristics: moisture not to exceed 2.5%; sulfur not to exceed 2.0%;volatile residue not to exceed 2.5%; ash not to exceed 8.0%; and carbonnot less than 85.0%.
 5. A combination according to claim 3 wherein thesolid pieces further comprising leftover revert materials from at leastone blast and/or electric arc furnace.
 6. A method of producing steelalloy in an electric arc furnace comprising the acts: introducing intothe electric arc furnace, while the furnace is operating, a firststeel-producing influent comprising solid cured and bound piecescomprising a combination of carbon materials; insuring that the curedand bound solid pieces predominantly comprising low value coal andfurther comprising coke breeze and/or petroleum coke. introducing intothe electric arc furnace salvage ferrous material, with flux.
 7. Amethod according to claim 6 wherein the low value coal comprises, byweight, 72-75% of the cured and bound solid pieces in the form of fixedcarbon.
 8. A method of making a high fixed carbon influent for anelectric arc furnace comprising the acts of: providing clean and crushedlow value coal as a first influent to a blender; providing coke as asecond influent to the blender; providing fixed carbon binder as a thirdinfluent to the blender; proportioning the coal to comprise 72-75% byweight and the coke 10-17% by weight in the blender, whereby the cokeacts as a temporary agent holding the ingredients together as asemi-solid conglomeration; blending the ingredients in the blender untilessentially homogeneous; forming the conglomerate into small solidpieces; firing the solid pieces to cure and bind them into high fixedcarbon pieces for introduction into the electric arc furnace to producesecondary steel.
 9. A method of obtaining a composite fixed carbonproduct for secondary steelmaking in an electric arc furnace comprisingthe acts of: mixing low value coal and a lesser amount of coke togetherwith a fixed carbon binder, the coke temporarily holding the mixturetogether as a semi-solid; forming the mixture into small semi-solidpieces; high temperature firing of the semi-solid pieces to cause themto bind and cure into fixed carbon pieces; introducing the fixed carbonsolid pieces together with scrap iron and/or steel into the electric arcfurnace whereby the fixed carbon solid pieces and the scrap form steelwithout pre-deterioration of the fixed carbon pieces.
 10. A methodaccording to claim 9 wherein the high temperature firing act comprisespre-heating the semi-solid pieces to a temperature on the order of 550°F., then in an anaerobic environment to a temperature on the order of1000° C. and anaerobically cooling the pieces.
 11. A low valuecoal-based composite source of fixed carbon in the form of cured andbound solid pieces for secondary steelmaking along with ferrous materialin electric arc furnaces, the solid pieces comprising particulate lowvalue coal in the range of 72-75% by weight, coke in the range of 10-17%by weight, a fixed carbon binder, the composite pieces being heat curedand reactively bound to prevent premature deterioration during secondarysteelmaking in the arc furnace and having a fixed carbon content in therange of 75-90% by weight.